The present invention relates to the field of microwave transmission, and in particular, to a microwave transmission apparatus in which adaptive code and modulation (adaptive code and modulation, ACM) is applied.
As shown in
In a microwave transmission apparatus 100 in which the ACM is applied, as a transmission capacity changes at any time along with changes of ambient factors such as the weather, to ensure the transmission quality and maintain a high bandwidth utilization ratio, the convergence module 12 is required to correspondingly change a service clock rate for transferring the multiplexed data. Accordingly, the ACM engine 18 is required to change parameters, such as a service modulation mode and an encoding rate, and initiate ACM switching.
During the ACM switching, the service clock rate at which the convergence module 12 sends the multiplexed data changes in different modulation modes, and correspondingly, a rate and a phase of a symbol clock generated by the intermediate frequency modules 14 and 15 in tracking the service clock rate also change, so a system clock generated by a receiver in tracking the symbol clock is unstable, so that the error rate of the service during the transmission is increased.
An embodiment of the present invention provides a microwave transmission apparatus, so that a stable system clock can be transferred between microwave transmission apparatuses.
A microwave transmission apparatus includes a first service transmitting device and a second service transmitting device which have a same function. The first service transmitting device includes a first multiplexing unit, and a first up conversion unit. The second service transmitting device includes a second up conversion unit, the first service transmitting device further comprises a first stream control unit, a first interface unit, a first encoding and mapping unit and a first clock tracking unit.
The first multiplexing unit is adapted to send, through the first stream control unit according to a service clock rate, multiplexed data generated by the first multiplexing unit to the first interface unit.
The first interface unit is adapted to writes the multiplexed data at the service clock rate, and reads the multiplexed data at a read clock rate, and transfers the multiplexed data to the first encoding and mapping unit.
The first encoding and mapping unit is adapted to perform, by using a symbol clock rate, encoding and mapping on the multiplexed data to generate symbol data, and send the symbol data to the first up conversion unit and the second up conversion unit.
The first clock tracking unit is adapted to generate the symbol clock according to a system clock, and perform frequency division on the symbol clock to acquire the read clock.
The first stream control unit is adapted to adjust the service clock rate according to a water line error generated by the first interface unit, so that the service clock rate is equal to the read clock rate, wherein when the service clock rate is inconsistent with the read clock rate, the first interface unit generates the water line error.
In the embodiment of the present invention, as a frequency and a phase of the system clock of the microwave transmission apparatus are fixed, even when ACM switching occurs, a frequency and a phase of the symbol clock generated by the clock tracking unit according to the system clock are still fixed, so that a receiver can generate a stable system clock by tracking the symbol clock, so as to stably transfer the system clock between microwave transmission apparatuses.
The following accompanying drawings are used for understanding of the embodiments of the present invention and do not serve as limitations on the present invention:
For persons of ordinary skill in the art to understand and implement the present invention, the embodiments of the present invention are described with reference to the accompanying drawings. Here, the exemplary embodiments of the present invention and the illustration thereof are used for explaining the present invention but do not serve as limitations on the present invention.
The convergence module 22 includes a multiplexing unit 222 and a stream control unit 224. The intermediate frequency module 24 includes an interface unit 242, an encoding and mapping unit 244, an up conversion unit 246, and a clock tracking unit 248. The convergence module 23 includes a multiplexing unit 232 and a stream control unit 234. The intermediate frequency module 25 includes an interface unit 252, an encoding and mapping unit 254, an up conversion unit 256, and a clock tracking unit 258.
As the corresponding functional units in the service transmitting devices 102 and 104 execute same functions, based on the principle of simplicity, in this embodiment, only the service transmitting device 102 is introduced in detail.
The multiplexing unit 222 multiplexes received services to generate multiplexed data and sends, at a service clock rate, the multiplexed data to the interface unit 242 through the stream control unit 224. The service includes a time division multiplex (time division multiplex, TDM) service and an Ethernet (Ethernet) service.
The interface unit 242 writes the multiplexed data at the service clock rate, and reads the multiplexed data at a read clock rate, and transfers the multiplexed data to the encoding and mapping unit 244. When the clock rates for reading and writing the multiplexed data are unequal, the interface unit 242 generates a water line error and sends the water line error to the stream control unit 224. For example, the interface unit 242 may be a first in first out (First in First out, FIFO) memory. When the FIFO memory writes the multiplexed data for the first time, as a read operation is not started yet, the interface unit 242 generates the water line error.
The stream control unit 224 adjusts the service clock rate according to the water line error, so that the clock rates at which the interface unit 242 reads and writes the multiplexed data are equal. For example, when the level rises, the stream control unit 224 decreases the service clock rate for sending the multiplexed data. When the level drops, the stream control unit 224 increases the service clock rate for sending the multiplexed data.
The clock tracking unit 248 generates a symbol clock according to the system clock of the microwave transmission apparatus 200, and performs, by using a frequency division factor M/N, frequency division on the symbol clock to acquire the read clock, that is, the M/N of the symbol clock is used as the read clock. The clock tracking unit 248 also provides the symbol clock for the encoding and mapping unit 244 and provides the read clock for the interface unit 242. For example, the clock tracking unit 248 includes a frequency synthesizer and a frequency divider. The frequency synthesizer generates the symbol clock according to the system clock of the microwave transmission apparatus 200. The frequency divider performs, by using the frequency division factor M/N, frequency division on the symbol clock to acquire the read clock.
The encoding and mapping unit 244 performs, by using the symbol clock, encoding and mapping on the multiplexed data to generate I and Q symbol data, and sends the symbol data to the up conversion units 246 and 256.
The up conversion units 246 and 256 perform, by using high-speed clocks, interpolation on the symbol data to generate number symbol streams, and implements interpolation conversion from the symbol clock to a sampling clock domain.
The radio frequency units 26 and 27 respectively convert the number symbol streams generated by the up conversion units 246 and 256 into analog signals, and modulate the analog signals into radio frequency signals and perform transmission, so as to support a 1+1 protection switching function.
The receiver receives and selects the multiplexed data, tracks the symbol clock carried in the multiplexed data to generate a system clock for use by the receiver, so as to finish the transfer of the system clock between the microwave transmission apparatuses 200.
As a frequency and a phase of a system clock of the microwave transmission apparatus 200 are fixed, even when ACM switching occurs, a frequency and a phase of the symbol clock generated by the clock tracking unit 248 according to the system clock are still fixed, so that the receiver can still generate a stable system clock by tracking the symbol clock, which enables transfer of a stable system clock between the microwave transmission apparatuses 200 and then reduces a bit error rate in the service transmission between the microwave transmission apparatuses 200.
In addition, the encoding and mapping unit 244 sends the symbol data generated after the encoding and mapping of the multiplexed data to the up conversion units 246 and 256, so as to avoid the result caused by the multiplexing unit 222 directly sending the multiplexed data to the interface units 242 and 252: as it is impossible to keep the levels of the interface units 242 and 252 completely the same, the interface units 242 and 252 respectively send two different water line errors to the stream control unit 224, which causes that the stream control unit 224 does not know which water line error should be used to adjust the service clock rate for sending the multiplexed data, and thereby causes control disturbance.
Further, the up conversion units 246 and 256 respectively use independent high-speed clocks as interpolation clocks, and the two high-speed clocks are not required to be synchronous, which avoids the hardware cost and complexity resulted from synchronization of primary and secondary high-speed clocks.
It should be noted that during a normal working process, the ACM engine 29, the multiplexing unit 232, the stream control unit 234, the interface unit 252, and the encoding and mapping unit 254 in the service transmitting device 204 do not work, and are triggered to work only when the primary and secondary roles of the service transmitting devices 202 and 204 are switched, so that the power consumption can be reduced.
The above descriptions are merely exemplary implementation manners of the present invention, but the present invention is not limited thereto. Any modification or replacement that can be easily figured out by any person skilled in the art within the technical scope disclosed in the present invention shall fall within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subjected to the protection scope of the claims
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